Skimming, pumping and suction
Skimming, pumping and suction are the major options in the event of an oil spill involving a fluid pollutant forming large accumulations. These operations encompass both the actual collection of the pollutant and the transfer of products collected, via an integrated tank or a discharge line, to a primary storage facility located on the upper beach or in the immediate vicinity. These techniques call upon means which are generally used in agriculture, sanitation or public works. However, specialised equipment also exists:
- Skimmers
- Pumps
- Vacuum systems
- Pneumatic conveying systems
Skimmers (datasheet)
Skimmers are specialised devices designed to skim the pollutant
from the water surface. They are made up of a floating skimming
head and a pump. There are a number of different types of
skimmers, which can be divided into two main categories
according to their functional mode:
- Mechanical skimmers
- Oleophilic skimmers
Pumps (datasheet)
Pumps can either be incorporated in the skimmer or connected
to it, or can alternatively be used with a simple floating
suction head. They function according to various principles,
which allow them to operate on petroleum products ranging
from fluid to highly viscous, with or without solids. On
the shoreline, the most commonly used pumps are screw pumps,
progressive cavity pumps, lobe pumps and peristaltic pumps.
Energy is supplied to the pumps by a thermal, hydraulic
or pneumatic power unit. Alternatively, the pumps can be
loaded onto a tractor equipped with a three-point hitch
for greater mobility.
Pumping is not always an option. Various factors determine
the feasibility of such operations as wells as the means
and methods required:
- the nature of the pollutant, in particular its viscosity
- agitation of the water body, which reduces outputs and selectivity, and hinders the deployment of the equipment
- the volume of pollutant accumulations, and more specifically their thickness. The thicker the slick, the more efficient the recovery operations, as they are more selective. Wherever possible, the pollutant should therefore be contained and moved towards the suction heads.
- the presence of solid debris which may impede the supply
to the pumps
- the morphology of the site storage facilities which could be set up in the immediate vicinity.
Vacuum
systems
These devices function by suction, produced by the vacuum
created in a recovery tank. The end of the suction hose
is directly placed in the slick, which must be thick enough.
Amongst the various types of vacuum systems can be listed:
- conventional vacuum systems as used in agriculture or sanitation. During the Amoco Cadiz disaster, hundreds of agricultural vacuum tanks were deployed on the beaches of Brittany, France.
- specialised vacuum units, of which several different types
have been developed especially for pollution response:
- heavy vacuum tanks mounted on a frame, mobile or otherwise, generally equipped with a floating suction head and a transfer pump to discharge the product collected
- light vacuum tanks, a French-designed concept, are mounted onto a frame with wheels. There are two tanks made of light, composite material connected to a single vacuum pump/compressor, alternately settling then evacuating the recovered pollutant.
- small portable backpack units were designed a few years ago and are most often made up of five small independent tanks connected to the same small vacuum unit.
Table comparing vacuum systems
Pneumatic
conveying systems
The principle behind pneumatic conveying systems depends
on the creation of a very high speed flow of air by a suction
unit. The vacuum initiates suction, but it is the flow which
pulls the oil, water and debris and transports them to the
system’s recovery tank.
-
Conventional pneumatic conveying systems, used by sanitation
trucks or for industrial cleaning, are fitted with a suction
hose, sufficiently large in diameter (125 -300 mm) that
it is practically impossible for the products pumped to
block it. The air flow should be continuous so that the
system functions correctly. The suction hose should be constantly
maintained slightly above the product to be recovered.
- Specialised pneumatic conveying systems are used more and more frequently on the shoreline. These are either small industrial suction pumps, or less powerful units but which do not systematically require a pneumatic compressor.
Table comparing pneumatic conveying systems
